Great, now I’m yawning too.

You know how yawning is contagious? That’s not just a human thing. Chimpanzees, several other primates, and possibly dogs can “catch” yawns from others of their own species. This strange effect might be a byproduct of empathy—not the complex empathy that involves understanding and sharing someone else’s suffering, but the reflexive empathy that makes you more likely to smile back at someone who smiles at you.

Empathy in social animals might hinge on familiarity or group membership: it’s something that you should do for your friends and family, but not for strangers. There are some studies claiming that humans are more empathic towards “ingroup” than “outgroup” individuals, as determined by skin colour; I’m more than a little skeptical of these. But chimps are a different story. Chimpanzees are extremely territorial, and they do in fact drive away strangers, while they’re more likely to need to cooperate with familiar individuals. So there’s reason to believe they should empathize more with “ingroup” chimps, and if they do, then perhaps this effect extends to contagious yawning.

Researchers showed videos (on iPods; I find this hilarious) of familiar or unfamiliar chimps either yawning or not to two groups of captive chimps. The chimps began to yawn more while watching videos of familiar chimps yawning, but not when they saw unfamiliar chimps yawning, nor the clips of either familiar or unfamiliar non-yawners. So not only do chimps “catch” yawns from other chimps, they do so when they see their friends yawning, but not strangers.

Notably, this “ingroup bias” hasn’t been found in humans: we’re just as likely to yawn after a stranger does as we are after an acquaintance. So this result may tell us little about empathy in humans. And, oddly, the same group of chimps yawned contagiously in response to animations of yawning chimps. What I’m dying to know is whether contagious yawning can transcend species boundaries. Want to participate in some research? Watch this video and see if you yawn!